Most current hydraulic transmissions use one or more two-way check valves for directing hydraulic pressure from either of two fluid sources to a hydraulically actuated component, such as a clutch, band, or spool valve. Hydraulic pressure is used in such a component to achieve and maintain some transmission function, such as a particular gear ratio. There are hydraulic elements (clutches or bands) corresponding to each gear ratio. The transmission shifts between different gear ratios by activation/deactivation of such elements. Activation of an element is accomplished when hydraulic pressure is directed to a particular element, typically by positioning one or more spool type valves or by direct control of the fluid by use of a solenoid actuated valve.
Previously, the spool valve was positioned by selection of a desired shift range by the vehicle operator, such as a selection of DRIVE, and another signal such as vehicle speed, throttle position, or engine manifold vacuum. Such a condition is common in current transmissions although in many modern transmissions a particular functional selection, such as OVERDRIVE or 2nd GEAR, may also be electronically selected under certain driving and loading conditions. Thus, there often are two hydraulic pressure sources for any one particular responding component. It is normally desirable to actuate such an element (such as a clutch) by only one of the two pressure sources at a time for consistency of control, but sometimes two sources are used together (in parallel) to achieve faster actuation.
Current two-way check valves utilize a spherical ball loosely contained in a cavity formed in the transmission's valve housing. The cavity has a pair of inlets and an outlets. Each inlet has seat portions or edges of an aperture against which the ball seats when in a closed operative position relative to that inlet. As the fluid enters at one inlet, the ball responds by moving to block the other inlet which is at a lower pressure. Consequently, the ball may have to move a relatively long distance into contact with the low pressure valve seat. Further, since the ball is traveling transversely to the seat, its inertia is likely to cause the ball to rebound therefrom and also to orbit or rotate relative to the seat. Either condition is undesirable because these characteristics cause slow and erratic performance and often result in relatively high by-pass leakages in addition to the by-pass leakage occurring during the period while the ball moves between the two seats and both inlets are open. Consequently, the lower-pressure inlet undesirably becomes a temporary outlet. A coordinated or synchronous opening and closing is desired. As the ball must move a relatively great distance and has high mass, the performance is poor and the associated transmission function may not be as consistent, or positive as possible. Also, at relatively low fluid flow rates, the ball responds poorly and often will not quickly or adequately seat and therefore seal an inlet. And because of the mass of the ball and its large shape, the flow rate suffers as the large ball does not get out of the way of the flow very quickly or efficiently. Further, the use of a ball type check valve restricts the inlet port to a circular shape and to a small diameter limited by the diameter of an associated ball which can be housed. Finally, the durability of a ball in this type of check valve is often marginal, especially if the inlet seat edge conditions are not well controlled and formed.
The subject application provides an improved two-way check valve which eliminates the previously used ball valve element. Instead, a onepiece flapper valve is provided. The flapper valve is generally V-shaped and formed with a crease or edge at a midposition. A pair of flat arm portions extend from the midportion away from the crease. In a transmission cavity, the creased portion supported between a pair of inlets and their seat portions. As the V-shaped valve element pivots about the crease, a surface of one of the arms covers one of the inlets and a surface of the other arm is raised away from the other inlet and its seat. Due to the V-shape, as one arm is forced away from its associated inlet seat, the other arm moves directly toward its associated inlet seat. This provides a coordinated and synchronous operation of the two ports. Further, the arm portions do not restrict the inlets to a relatively small circular shape. In addition, the thin arm portions have a low mass and are capable of rapid movement between opened and closed positions. The low mass, large area flapper valves also react desirably and positively in response to low flow rates. Also, the arm portions need only travel a short distance which increases the responsiveness of the check valve. Further, the arm portions contact a relatively large area of easily controlled surface quality about the inlet seats to enhance durability and provide desired positive sealing without rebound or orbiting as was common with ball valves.
Other features, objects, and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings and claims.